In hauling containers for transporting scrap, waste, or for recycling purposes, and so forth, it is common to employ roll-off trailers. With such a trailer, a portion of the structure remains horizontally oriented and connected to the axles and cab or tractor by way of a king-pin assembly, whereas a second portion of the structure pivots upwardly from a rearward joint, enabling the containers to be pulled up and onto the trailer from the ground, transported, unloaded and/or dumped. To facilitate the unloading procedure, the pivoting portion is again raised up, enabling the container(s) to roll off and back onto the ground, hence the name "roll-off" trailer.
There are many different types and styles of roll-off trailers in service today, depending upon the application at hand. For light-duty applications, a single-container or "one-box" design may be sufficient, and may employ only a few axles. Such a configuration would be suited, for example, to the short-distance hauling of smaller roll-off style containers. On the other end of the spectrum, for long-distance hauling of very heavy materials, a multi-axle "two-box design" could instead be employed. Benlee, Inc., the assignee of this application, manufacturers a full range of such trailers, and examples thereof are provided in its catalog.
One potentially undesirable feature of the conventional roll-off design concerns the fact that the framework used to load and unload the containers must be pivoted at a pronounced angle with respect to the ground in some cases, resulting in weight-balancing considerations, particularly if a full, heavy container is pulled to the greatest extent possible on a frame at its most pronounced elevation. The two-box design presents further engineering challenges, since it is impractical, if not unsafe, to build a framework capable of pulling two containers all the up an incline before lowering the frame back onto the horizontal trailer structure. For this reason, two-box trailer designs have evolved separately, and usually include a rear portion which inclines in combination with some mechanism for moving the first loaded box forwardly toward the cab, at which time the rear portion may again be inclined so as to receive the second container. Unloading is essentially carried out with a reverse process. U.S. Pat. No. 5,246,330 describes one of many such two-box designs.
Regardless of trailer type, in the roll-off industry, as with many trucking applications, trade-offs exist between performance and weight. While it might be advantageous to build trailers with the strongest possible members and the greatest variety of operational modes, the hydraulic cylinders, winches, and other drive means add considerable weight. This additional weight not only affects fuel economy, but different states place different upper limits on load carrying capacity, such that the heavier the trailer, the less it may be able to carry, thereby defeating its intended purpose. Two-box styles are particularly susceptible to weight problems, since both the underlying portion which remains horizontal and the part which pivots to load and unload the containers must be very substantial and so must the hydraulic cylinders and other operational components involved. As such, any improved design capable of maintaining or enhancing performance in the roll-off industry would be welcomed, particularly if, at the same time, the resulting empty or "tare" weight is maintained or, ideally, reduced.